There is an increasing usage of water soluble polymers and copolymers in wastewater treatment industries. These compounds have shown desirable utility for the purpose of dewatering sludge and clarifying contaminated water.
When paint is detackified in a wet paint spray booth recirculating water system, the killed paint forms a sludge that may disperse, sink, or float in the system. It is important, in most systems, that the treated paint be removed from the water as quickly and as efficiently as possible. A build up of treated paint could cause foaming problems and reduce the effectiveness of the detackification program. The detackification program should control dispersion, sinking or floating of the killed paint.
Paint spray booth sludge water typically includes resin, pigment, some soluble solvent and paint detackification treatment chemicals. Solids generally range from about 0.5% to 50%. The sludge may result from detackified solvent based and/or water based paints. The pH of the paint spray booth sludge water will depend upon the pH of the detackification program and will generally fall between 6.0 and 12.0. However, it would more probably fall between 7.0 and 9.0.
The treatment of the sludge is dependent upon the design of the sludge removal system. Most often, the sludge is transferred to a separate unit designed to float and dewater the sludge. A high molecular weight polymer is fed directly to this unit to enhance flotation and coagulation, which produces a disposable sludge that is high in solids. The dryness of the sludge is critical to the cost of disposing it. Its classification as hazardous or non-hazardous waste is also dependent on the dryness of the sludge. Paint booth sludge is generally sent to a landfill.
The efficacies of the polymers or copolymers used will vary depending upon the type of monomers chosen to form the polymer or copolymer, the molecular weight of the synthesized molecule and, in the case of a copolymer, the placement of the selected monomers on the backbone of the copolymer. It is the latter characteristic that is the focus of the present invention.
High molecular weight emulsion polymers have been successful in dewatering paint spray booth sludge. This invention describes novel high molecular weight polymers that have proven to be more effective than the currently used emulsion polymers. These polymers are novel in that the charged quaternary nitrogens are primarily on the grafts rather than on the backbone of the polymer. The distribution of the charge has made a dramatic difference in the amount of polymer required to float and coagulate the paint sludge.
Polymers with long sequences of two monomers can be categorized as block copolymers or graft copolymers. In graft copolymers sequences of one monomer are "grafted" onto a "backbone" of the second monomer type, ##STR3##
It is an object of this invention to prepare distinctive water soluble graft copolymers for paint sludge dewatering applications.